Preheat the oven: Set your oven to 400°F (200°C). Line a baking sheet or 9x13-inch baking dish with parchment for easy cleanup.

Prep the zucchini: Trim the ends, slice each zucchini lengthwise, and use a spoon to scoop out the centers, creating boats. Leave about 1/4-inch border so they hold their shape. Chop the scooped zucchini flesh and set aside.

Season and par-bake: Brush the zucchini boats with olive oil, sprinkle with salt and pepper, and place them cut side up. Bake for 10–12 minutes to soften slightly.

Cook the beef: While the zucchini bakes, heat a large skillet over medium-high heat. Add a drizzle of oil, then the onion. Cook 3–4 minutes until softened. Add garlic and cook 30 seconds.

Brown and season: Add the ground beef. Break it up and cook until browned, 5–7 minutes. Drain excess fat if needed. Stir in taco seasoning and tomato paste. Cook 1 minute to bloom the spices.

Add moisture and mix-ins: Stir in the chopped zucchini flesh and the fire-roasted tomatoes (drained). Cook 3–4 minutes until most liquid evaporates. Fold in black beans or corn if using. Taste and season with salt and pepper.

Fill the boats: Remove zucchini from the oven. Spoon the beef mixture into each boat, packing it in. Top with shredded cheese.

Bake to finish: Return to the oven for 8–10 minutes, until the cheese is melted and the zucchini is tender but not mushy.

Garnish and serve: Sprinkle with cilantro or green onions. Squeeze fresh lime over the top. Add salsa, avocado, or a dollop of sour cream if you like.